[Bugfix] Include entry-point logits processor plugins in output token…

[YingxuH]

Purpose

Fix entry-point logits processor plugins (vllm.logits_processors group) being silently ignored when computing the logitsprocs_need_output_token_ids flag in gpu_model_runner.py.

Previously, the flag was derived solely from bool(custom_logitsprocs), which only reflects CLI-passed processors. Entry-point plugins loaded by build_logitsprocs() → _load_logitsprocs_plugins() were not accounted for. When the flag was False and all penalties were neutral (repetition_penalty=1.0), vLLM's async scheduling path filled the output token ID buffer with -1 placeholders instead of real tokens, silently breaking any entry-point logits processor that inspects generation history (e.g., n-gram repetition prevention).

Changes:

• state.py: Add has_custom keyword-only parameter to LogitsProcessors.__init__ (defaults to False, backward-compatible).
• __init__.py: build_logitsprocs() sets has_custom=bool(custom_logitsprocs_classes), where custom_logitsprocs_classes includes both entry-point plugins and CLI-passed processors.
• gpu_model_runner.py: Extract build_logitsprocs() result into a local variable and derive the flag from logitsprocs.has_custom or self.vllm_config.reasoning_config is not None.

Test Plan

New test file tests/v1/logits_processors/test_entrypoint_output_token_tracking.py with 3 test cases, reusing existing mock utilities from tests/v1/logits_processors/utils.py:

# New tests
python -m pytest tests/v1/logits_processors/test_entrypoint_output_token_tracking.py -v

# Existing correctness tests (regression check)
python -m pytest tests/v1/logits_processors/test_correctness.py -v

Test Result

Built from source on H100 (CUDA 12.8, Python 3.12, PyTorch 2.10):

tests/v1/logits_processors/test_entrypoint_output_token_tracking.py::test_entrypoint_plugin_enables_output_token_tracking PASSED
tests/v1/logits_processors/test_entrypoint_output_token_tracking.py::test_cli_logitsprocs_still_enable_tracking PASSED
tests/v1/logits_processors/test_entrypoint_output_token_tracking.py::test_no_logitsprocs_disables_tracking PASSED

tests/v1/logits_processors/test_correctness.py::test_logitsprocs[logitsprocs_under_test0-50-cuda:0] PASSED
tests/v1/logits_processors/test_correctness.py::test_logitsprocs[logitsprocs_under_test1-50-cuda:0] PASSED
tests/v1/logits_processors/test_correctness.py::test_logitsprocs[logitsprocs_under_test2-50-cuda:0] PASSED
tests/v1/logits_processors/test_correctness.py::test_logitsprocs[logitsprocs_under_test3-50-cuda:0] PASSED
tests/v1/logits_processors/test_correctness.py::test_logitsprocs[logitsprocs_under_test4-50-cuda:0] PASSED
tests/v1/logits_processors/test_correctness.py::test_logitsprocs[logitsprocs_under_test5-50-cuda:0] PASSED

---

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[gemini-code-assist]

Code Review

This pull request fixes a bug where entry-point logits processor plugins were not correctly enabling output token ID tracking. Previously, the logitsprocs_need_output_token_ids flag was only determined by CLI-passed custom logits processors, leading to -1 placeholders in the output token ID buffer for entry-point plugins. The fix involves modifying the LogitsProcessors class to explicitly track whether any custom (CLI-passed or entry-point) logits processors are loaded via a new has_custom attribute. The build_logitsprocs function is updated to pass this flag, and in gpu_model_runner.py, the logitsprocs_need_output_token_ids flag is now correctly derived from LogitsProcessors.has_custom, ensuring both types of plugins are considered. A new test file test_entrypoint_output_token_tracking.py has been added to verify this corrected behavior. I have no feedback to provide.

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[YingxuH]

@njhill @llsj14 Friendly ping — this has been open for 5 days. The fix touches the same logitsprocs_need_output_token_ids flag that #20859 (ThinkingTokenBudget) modified. Just rebased onto latest main. Happy to address any feedback.

[njhill]

Thanks @YingxuH. LGTM, just one comment.

[YingxuH]

@njhill Addressed your feedback 8 days ago — is there anything else needed from my side?